The present application relates to a top-mounted stirring apparatus with a stirring shaft, a drive, stirring tool and contactless coupling for transmitting drive movement from the drive through the stirring apparatus shaft to the stirring tool. The apparatus is to be mounted on the upper wall of the vessel.
Stirring apparatus of this general type are known in the art. They are formed as for example as permanently magnetic rotary stirring apparatuses. The rotary transmission between the drive motor and the stirring shaft operates in accordance with the principle of the magnetic radial coupling. The outer coupling part is connected with an electric motor having a steplessly regulatable transmission and displaces the inner coupling part through an air gap into a rotary movements in synchronous with the transmissions. Alternatively, hydraulic, pneumatic or other types of transmission can be used. A gap pipe composed of paramagnetic material is arranged in the air gap between the inner and outer coupling parts. It can be connected for example through a cooling column with an autoclave inner chamber while the inner drive system is pressure-tightly closed from the autoclave inner chamber. The cooling column therefore separates the high autoclave temperatures from the magnetic system and the bearing.
The gap pipe with the subsequent cooling column together with the autoclave inner chamber represents a joint volume. Since inside the cooling column the stirring shaft is arranged and supported with respect to the gap pipe, a seal must be provided inside the gap pipe and the connected cooling column. It separates the autoclave chamber from the volume of the gap pipe or cooling pipe so that the stirrer bearing is protected from the autoclave atmosphere. The rotatable stirring apparatus shaft extends through the seal into the autoclave inner chamber. The bearing of this freely extending shaft end poses certain problems since the shaft can be easily deflected under the reaction forces and has tendency to vibrations.
In particular, for performing the microbiological processes, the seals between the rotatable stirring shaft and the stationary gap or cooling pipe must not be compromised. The result can be the loss of the whole charge.
The seals and bearings in the known magnetic stirring apparatus always constitute weak points and act especially disadvantageously in aseptic and sterile applications. The upper part of the gap pipe or the cooling pipe has without ventilation a constant air cushion which cannot be sterilized or is sterilized insufficiently in the autoclaves. The bearing also cannot be lubricated. Without suitable bearing, however, the stirring shaft cannot be formed substantially long. The bearing provided in the gap pipe and the seals form uncontrollable regions in which microorganisms can deposit. Even expensive seals with blocking medium cannot satisfactorily solve these problems.